1. Field of the Invention
This invention generally relates to a data transmission structure and method and, more particular, to a frequency calibration device and method for automatically calibrating the oscillation frequency of a programmable oscillator according to a data stream.
2. Description of the Related Art
An oscillation circuit with external clock can be used to provide a clock signal, and the oscillation circuit conventionally uses an external precise clock component, such as a crystal resonator or a ceramic resonator, to provide a reference frequency to the oscillation circuit. However, the external precise clock component not only increases the system cost, the control chip of the oscillation circuit also needs one or two extra pins to be served as a communication interface to the precise clock component.
In addition to using the reference frequency provided by the external precise clock component, the control chip can also use such as a phase locked loop (PLL) or a delay locked loop (DLL) to match the internal frequency thereof with the data rate of received data stream. However, this method usually takes longer calibration time and thus is adapted to certain applications, such as USB devices.
Accordingly, it is necessary to provide a frequency calibration device and method that does not require an external precise clock component and can calibrate the oscillation frequency of a programmable oscillator quickly and automatically so as to solve the problems in the art.